1. Field of the Invention
This invention relates to a heat-sensitive transfer medium that can form sharp color transferred patterns having a superior rub resistance.
2. Related Background Art
Recording processes and recording apparatus suited for individual information processing systems have been developed with the progress of information industries. As one of such recording processes, thermal recording has been recently put into wide use because the apparatus used can be compact and noiseless and has superior operability and readiness for maintenance care. This thermal recording is a process in which a heat-sensitive transfer medium is heated by means of a thermal recording head and a transfer pattern is transferred to a recording medium to obtain a record.
As heat-sensitive transfer mediums used therein, those comprising a base material and an ink layer formed thereon and largely containing a wax were prevailing in the past. However, transferred patterns formed using heat-sensitive transfer mediums having such a structure also largely contain the wax, and hence the transferred patterns may be defaced when rubbed, having a poor rub resistance. After that, in order to improve rub resistance, a heat-sensitive transfer medium has been developed which comprises a base material and, provided thereon, a release layer and an ink layer largely containing a resin. This release layer is provided so that the ink layer can be released and transferred with ease, and is chiefly composed of wax or the like. Also, in this release layer, the gram number of solid content per unit square meter when dried (herein called "coating weight") is commonly from about 0.8 to 4.0 g/m.sup.2. However, when patterns are transferred using the heat-sensitive transfer medium of this type, the wax in the release layer moves to the ink layer when heated, and hence the rub resistance originally possessed by the ink layer may become poor to make it impossible to form transferred patterns having the desired rub resistance.
To overcome such a disadvantage, a heat-sensitive transfer medium has been developed which has a structure wherein an intermediate layer chiefly composed of a resin is provided between a release layer and an ink layer so that the wax in the release layer does not come into the ink layer.
Meanwhile, in recent years, there is an increasing demand for color printing that can form transferred patterns in colors. This color printing is a process in which transfer layers having different colors are superimposed to make an image. When a color transferred pattern is formed using the heat-sensitive transfer medium made up to have the intermediate layer described above, the layer contiguous to the surface of an underlying transfer layer is the release layer chiefly composed of wax. Hence, when two or more transfer layers are superimposed, what is called "trailing" and "smearing" may occur, the former being caused when a color of the upper layer of a transferred pattern spreads to make lines and the latter when a color of the lower layer spreads. Also, compared with transferred patterns formed using what is called a resin type heat-sensitive transfer medium, transferred patterns may have a very poor rub resistance, thus the color printing can not be practical in some cases.